The　adsorption　of　ethylene　on　FeO(100)　surface　has　been　studied　with　a　periodic　slab　model　by　PW91　of　GGA　within　the　framework　of　the　density　functional　theory.　The　calculated　results　indicated　that　ethylene　adsorption　on　the　surface　hollow　site　forming　double　or　bonds　was　the　most　favorable　structure　with　the　predicted　adsorption　energy　of　86.8　kJ/mol.　The　analysis　of　density　of　states,　charge　population,　orbitals,　and　vibrational　frequencies　before　and　after　the　adsorption　showed　that　Fe　3d　electrons　donated　to　the　anti-bonding　pi　orbital　of　ethylene　and　the　adsorbed　ethylene　rehybridized　from　sp(2)　to　sp(3)　partly.